Currently, most vaccines are administered parenterally with consequent problems arising from the invasive nature of the administration route. For instance, it has been proposed, in U.S. Pat. No. 4,157,390, to use red blood cells as vehicles for the presentation of enteropathogenic antigens in a parenteral vaccine administered to prepartum sows. A disadvantage of parenteral administration is that, in general, it induces a better blood borne immune response than a mucosal one, yet the prophylaxis or treatment of some infective agents is more appropriately dealt with by a strong mucosal immunity. The parenteral nature of prior art vaccines has not in general resulted in a strong mucosal response.
To redress some of these problems, orally administered vaccines have been proposed against various infective agents. Unfortunately as the alimentary tract provides a hostile environment, it is only fortuitously, such as in the Sabin vaccine, that these have been effective.
It is an object of the present invention to provide a vaccine, appropriate for oral administration, which redresses some of the disadvantages experienced in the past.